Computing devices, such as notebook computers, personal data assistants (PDAs), and mobile handsets, have user interface devices, which are also known as human interface device (HID). One user interface device that has become more common is a touch-sensor pad. A basic notebook touch-sensor pad emulates the function of a personal computer (PC) mouse. A touch-sensor pad is typically embedded into a PC notebook for built-in portability. A touch-sensor pad replicates mouse x/y movement by using two defined axes which contain a collection of sensor elements that detect the position of a conductive object, such as finger. Mouse right/left button clicks can be replicated by two mechanical buttons, located in the vicinity of the touchpad, or by tapping commands on the touch-sensor pad itself. The touch-sensor pad provides a user interface device for performing such functions as positioning a cursor, or selecting an item on a display. These touch-sensor pads can include multi-dimensional sensor arrays. The sensor array may be one dimensional, detecting movement in one axis. The sensor array may also be two dimensional, detecting movements in two axes.
FIG. 1 illustrates an example of a capacitive touchpad device 100. The touchpad 100 includes a substrate with multiple layers. The layers include rows of conductive traces 102, followed by an insulating layer (not shown), followed by columns of conductive traces 104, followed by another insulating layer (not shown) and a ground plane (not shown).
By being in proximity or in contact on a particular portion of the array, the capacitance between the conductive lines and ground varies and can be detected. By sensing both rows 102 and columns 104, the position of the changing capacitance can be pinpointed. For example, a stylus or a user's finger contacting on the touchpad at location 1 generates signals 106 on the vertical axis 108. Signals 106 are detected using the rows of conductive traces 102. A stylus or a user's finger contacting on the touchpad at location 2 generates signals 110 on the horizontal axis 112. Signals 110 are detected using the columns of conductive traces 104.
Each conductive trace is connected to a respective pin. The pins are connected to an electrical component (not shown) that controls and detects the signals from the array. Therefore, the total number of pins required is equal to the number of rows of conductive traces 102 and the number of columns of conductive traces 104. It would be desirable to reduce the number of pins.